The present invention relates to displacing oil within a subterranean reservoir by injecting steam and steam-foaming surfactant. More particularly, the invention relates to injecting a pretreating fluid ahead of at least some of the steam and steam-foaming surfactant, for increasing the rate of surfactant transport and decreasing the amount of surfactant needed.
Numerous processes have been developed for displacing oil within a subterranean reservoir by injecting mixtures of steam and steam-foaming surfactants. For example, U.S. Pat. No. 4,086,964 R. E. Dilgren, G. J. Hirasaki, D. G. Whitten and H. J. Hill describes such a process for steaming a reservoir susceptible to gravity override until a steam breakthrough from injection to production wells is at least imminent then injecting a steam-foam-forming mixture of steam, noncondensible gas, aqueous electrolyte and steam-foaming surfactant, to maintain an increased pressure within the steam channel without plugging or fracturing the reservoir. U.S. Pat. No. 4,393,937 by R. E. Dilgren and K. B. Owens describes a process for displacing oil within a subterranean reservoir by injecting a steam-foam-forming composition comprising steam, noncondensible gas, aqueous electrolyte and olefin sulfonate surfactant. The disclosures of those patents are incorporated herein by reference.